Comprehensive Income and Accumulated Other Comprehensive Income - Reclassification Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains on investments	$ 258	$ 738
Income before income taxes	21,535	21,422
Income tax expense	(4,196)	(4,091)
Net income	17,339	17,331
Unrealized Gains (Losses) On Debt Securities, Net Of Tax [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains on investments	(6)	393
Income before income taxes	(6)	393
Income tax expense	1	(83)
Net income	$ (5)	$ 310